1. Field of the Invention
The present invention relates to manufacturing a plurality of optical fiber ribbons formed by applying coating resin in a lump to coated optical fibers arranged in parallel on one and the same plane, and a separable optical fiber ribbon formed by further integrally applying coating resin to the optical fiber ribbons arranged in parallel on one and the same plane. Particularly, the present invention relates to a collectively coating die device for manufacturing an optical fiber ribbon and a separable optical fiber ribbon, a manufacturing device having such a collectively coating die device for manufacturing a separable optical fiber ribbon, and a method of manufacturing such a separable optical fiber ribbon.
2. Description of the Conventional
Conventionally, to manufacture a separable optical fiber ribbon shown in FIG. 5A by way of example, constituted by a plurality of coated optical fibers are coated integrally, a die device having a branch portion 30a shown in FIG. 8 is known, as disclosed in Unexamined Japanese Patent Publication (kokai) No. Hei. 3-150519.
However, there is a problem in a method of manufacturing a separable optical fiber ribbon with such a die device having a branch portion as disclosed in the above-mentioned publication. That is, when the line speed increases, the arrangement of coated optical fibers 1 in a separable optical fiber ribbon 26 may fall into disorder as shown in FIG. 5C, and in some cases, there occur so-called fault of fiber planarity in the coated optical fibers 1 due to the displacement of the coated optical fibers 1 from the positions on one and the same plane on a large scale.
With such fault of fiber planarity, it becomes impossible to mount the coated optical fibers 1 of the separable optical fiber ribbon 26 onto V-grooves of a V-grooved board properly in an cable installation step or the like, so that it is difficult to connect the coated optical fibers 1 by fusion splice. Further, there is a fear that the fault of fiber planarity causes increase of transmission loss. It is therefore extremely important to suppress such fault.
Specifically, as shown in FIG. 6, the displacement .DELTA.a-.DELTA.f of the center of each of the coated optical fibers 1 disposed in the separable optical fiber ribbon 26 relative to the straight line L connecting the respective centers of the coated optical fibers 1 disposed in both ends of the separable optical fiber ribbon 26 is referred to as a fiber planarity. It is necessary to make the respective fiber planaritys as small as possible.
Particularly, recently, the production technique has been improved so that the line speed is increased conspicuously. Therefore, the problem that fault of fiber planarity is increased has become manifest.
The present inventor investigated the cause of this problem and found out the following fact. In a step of manufacturing optical fiber ribbons, in a collective resin coating method using such a collectively coating die device having a branch portion 30a as shown in FIG. 8 by way of example, unstable vortex flows J of coating resin appear in the branch portion 30a in the direction reverse to the moving direction of the coated optical fibers 1 so as to disturb self-centering force generated in the coating resin in the collectively coating die device. Consequently, the fault of fiber planarity is increased.
Generally, when a linear body is passed through a die having a tapered portion and storing a liquid, a drag flow is generated in the liquid with the passage of the linear body. This drag flow makes a force to act on the linear body to dispose the linear body at the center of the die, that is, self-centering force.
Therefore, generally, when optical fibers pass through optical fiber passageways, respectively, of the collectively coating die device 2 filled with liquid-type coating resin, such self-centering force acts on the optical fibers so that the optical fibers are disposed at the center of an outlet opening 35.
The present inventor has found out the following fact. When the conventional collectively coating die device shown in FIG. 8 is used, a resin flow moving in the moving direction of the optical fibers collides with the branch portion 30a to generate unstable vortex flows J when the line speed of the optical fibers increases, and these vortex flows J disturb the self-centering force to cause the fault of fiber planarity. The present inventor has given light onto a structure of a die device which can eliminate such vortex flows to thereby achieve the present invention.